Coastal flood talk? Not today…:

Coastal flood talk? Not today… Just a few refresher slides…
I have 100s of coastal flood slides if you choose to abuse yourself

Water Level Prediction Nomogram:

Water Level Prediction Nomogram Users/Emergency managers (and others) could choose to use the interactive feature (“slider bars”) – on a web site
Education/disclaimer would be needed
Non-interactive display could be introduced first
Should be used daily: not shelved for the twice a year events

We have two models…:

Summary of ET Storm Surge Guidance:

GoMOOS Water Level Prediction:

GoMOOS Water Level Prediction Should use storm surge guidance
Should be an ensemble? (use two operational storm surge models)
How should this combination be applied?
60% weighted GFS model?
40% weighted NGM model?
Why choose these initial numbers???...

Error of the GFS (MRPSSE Product) Portland Harbor:

Error of the GFS (MRPSSE Product) Portland Harbor Data included an average of 2 storm surge products prior to coastal flood event
Most back to back runs were nearly identical!
The MRPSSE bias varied much more than the MRPECS product.
The MRPSSE product under-predicted 7 surge events and over-predicted 4.
Data range: -1.10’ - +0.61’; Average bias was -.3 feet.
[GFS surge Guidance available at: http://www.weather.gov/mdl/etsurge/index.htm]

Error of the NGM (MRPECS Product) (Portland Harbor):

Error of the NGM (MRPECS Product) (Portland Harbor) Data limited to 15 coastal flood events using the MRPECS product
Data included an avg. of 2 storm surge forecasts immediately prior to the coastal flood
All back to back model runs (00Z and 12Z) were nearly identical (this is good!)
12 of 15 showed a model over-forecast surge bias (2 forecasts hit the mark)
Data range: -.2’ to +1.2’; Average bias was +.38 feet.

Merging of Storm Surge Models: An Ensemble :

Merging of Storm Surge Models: An Ensemble Usually in meteorology…ensembles outcome provides the most likely solution
May need additional verification
Is there any other known verification out there at all????

Statistical Wave Spectrum:

The Role of “Wave Set-up”:

The Role of “Wave Set-up” Here’s the kicker...”Wave setup” is the water rise at the coast due to breaking waves on the beach.
Basically - - potential energy of large ocean waves is converted into the kinetic energy required to maintain an anomalous surge of water near the shoreline.

Other Secondary Effects: Breaker Run-up Assists Splash-over:

Other Secondary Effects: Breaker Run-up Assists Splash-over On any beach there is a “spectrum” of waves…
Most crashing waves run up the slope generally about the same distance.
Periodically however, a wave will crash and run up the beach much higher than the average waves. This can cause “splash-over”.
The highest 2 % breaker run-up can be mathematically computed (Water rise ~ 1/2 the predicted breaking wave height plus 50 cm) Breaker run-up Splash-over (York Beach, Maine)

Supporting documentation (NWS GYX coastal flood study)… :

Large waves are associated with major flooding:

Large waves are associated with major flooding

GoMOOS Diagram:

GoMOOS Diagram Water level prediction:
Forecast Total tide from the NGM and GFS models (astronomical tide +/- surge) versus…
Forecast offshore wave height (SWAN)
- some adjustments may need to be made to forecast wave height at the beach